Hereinafter a Carrier will be briefly described.
A user may include information that the user wishes to transmit by performing modulation operations on amplitude, frequency, and/or phase of a sine wave or a periodic pulse wave. At this point, the sine wave or pulse wave, which performs the function of carrying information, is referred to as a carrier.
Methods for modulating carriers may include an SCM (Single-Carrier Modulartion scheme) or an MCM (Multi-Carrier Modulation scheme). Herein, the Single-Carrier Modulation scheme (SCM) refers to a modulation scheme, wherein all types of information is loaded in a single carrier and then modulated.
The Multi-Carrier Modulation scheme refers to a modulation technique that can divide a whole Bandwidth Channel of a single carrier into multiple sub-channels each having a small bandwidth and that can perform multi-transmission through a plurality of narrowband Sub-Carriers.
At this point, when using the Multi-Carrier Modulation (MCM) scheme, each sub-channel may be approximated to a Flat Channel fur to the small bandwidth. Additionally, the user may compensate for any channel distortion by using a simple equalizer. Furthermore, high-speed implementation of the Multi-Carrier Modulation scheme may be performed by using Fast Fourier Transform (FFT). In other words, the Multi-Carrier Modulation scheme is more advantageous in high-speed data transmission as compared to the Single-Carrier Modulation (SCM) scheme.
As the functions of base stations and/or user equipments evolve, the frequency bandwidth that can be provided by or used in the base stations and/or user equipments is expanding. Therefore, according to the exemplary embodiments of the present invention, the present invention discloses a multi-carrier system that supports wideband by performing Carrier aggregation, wherein one or more carriers are combined and used (or aggregated).
More specifically, unlike the above-described Multi-Carrier Modulation Scheme, wherein a single carrier is divided and shared, the multi-carrier system that will be described below corresponds to the case when one or more carriers are combined (or grouped) and used.
In order to efficiently use the Multi-Band (or Multi-Carrier), a technique of having a single Medium Access Control (MAC) entity manage multiple carriers (e.g., multiple Frequency Carriers (FCs)) has been proposed.
(a) and (b) of FIG. 1 illustrate a method for transmitting and receiving multiple bandwidth Radio Frequency (RF) based signals.
As shown in FIG. 1, in the transmitting end and in the receiving end, in order to efficiently use multiple carriers, one Medium Access Control (MAC) layer may manage multiple carriers. At this point, it is assumed that, in order to efficiently transmit and receive multiple carriers, the transmitting and the receiving end can transmit and receive all of the multiple carriers. At this point, since the Frequency Carriers (FCs), which are managed by a single Medium Access Control (MAC) layer, are not required to be contiguous to one another, this technique is more flexible in the aspect of resource management. More specifically, Contiguous Aggregation and Non-contiguous Aggregation may both be performed.
Referring to (a) and (b) of FIG. 1, Physical Layer (PHY) 0, Physical Layer (PHY) 1, . . . Physical Layer (PHY) n-2, Physical Layer (PHY) n-1 indicate the multi-band according to technique of present invention, and each band may have a frequency carrier (FC) size, which is assigned for a specific service based upon a pre-decided frequency policy. For example, Physical Layer 0 (RF carrier 0) may have a frequency carrier (FC) size, which is assigned for general FM radio broadcasting, and Physical Layer 1 (RF carrier 1) may have a frequency carrier (FC) size, which is assigned for mobile phone communication.
As described above, depending upon the characteristics of each frequency band, each of the frequency bands may have a different frequency band size. However, in the following description, it is assumed that each frequency carrier (FC) has a size of A [MHz]. Also, each frequency allocation band may be represented as a carrier frequency enabling each frequency band to use a baseband signal. Hereinafter, each frequency allocation band will be referred to as a “Carrier Frequency Band” or, when there is no confusion, each frequency allocation band will be merely referred to as a “Carrier”, which represents each carrier frequency band. Furthermore, as in the recent 3GPP LTE-A, the above-described carrier may also be referred to as a “component carrier” in order to be differentiated from the subcarrier, which is used in the multi-carrier scheme.
In this aspect, the above-described “Multi-Band” scheme may also be referred to as a “Multi-Carrier” scheme or a “carrier aggregation” scheme.
In order to transmit a signal through a multi-band, as shown in (a) of FIG. 1, and in order to receive a signal through a multi-band, as shown in (b) of FIG. 1, the transmitter/receiver is/are required to include a radio frequency (RF) module, which is configured to transmit and receive signals through all of the multi-band. Also, referring to FIG. 1, a configuration method of “Medium Access Control” is decided by the base station regardless of a downlink (DL) and an uplink (UL).
In short, the technique of the present invention refers to a technique for transmitting/receiving signals by having a single medium access control entity to manage/operate multiple radio frequency carriers (RF carriers). RF carriers being managed by a single medium access control are not required to be contiguous to one another. Therefore, according to the technique of the present invention, the multi-band scheme is advantageous in that it is more flexible in the aspect of resource management.
FIG. 2 illustrates an exemplary method for allocating a frequency in a multi-carrier system.
Referring to FIG. 2, frequency carrier 0 to frequency carrier 7 may be managed by radio frequency 0 to radio frequency 7. Also, as shown in the example shown in FIG. 2, it is assumed that frequency carrier 0, frequency carrier 2, frequency carrier 3, frequency carrier 6, and frequency carrier 7 are already assigned to each specific conventional communication service. Meanwhile, available frequency carrier 1, frequency carrier 4, and frequency carrier 5 may be effectively managed by a single medium access control (medium access control #5). Herein, as described above, since the frequency carriers configuring a single medium access control are not required to be contiguous to one another, the frequency resource may be more effectively managed.
However, the above-described multi-band based communication scheme may only be defined more or less conceptually, and, whenever required, the multi-band based communication scheme may be understood as a method wherein merely more frequency carriers are additionally assigned. Therefore, an efficient method for transmitting and receiving signals that enables high-performance processing, and, more particularly, a method for transmitting and receiving control information, which newly or additionally assigned a carrier to the user equipment, or which manages the assigned carriers is required to be defined more specifically.